That would be N3333E "Glamorous Glenn III", which does have gun ports (though quite likely replica barrel tips only). It does not have the shell ejector chute openings, which is another detail that is sometimes referenced in possibly adding to the whine/whistle dynamics.
I remember reading once, from I believe Dudley Henriques, that the "distinct" Merlin sound, as he referenced it, was achieved when using the max military continuous/climb power setting of 46" MP and 2,700 RPM, and referenced using those power settings in airshow displays. Of course in cruise flight the power is quite reduced from that, especially if the pilot decides to really bring it back to max economy (there is a range of cruise settings, all the way from "economy-cruise" up to "climb-cruise", and various pilots/operators have their own desired settings). I've had the fortunate experience of having a Mustang based near me for some years, and it wasn't always as apparent flying overhead when the power was way back compared to when it was climbing out and still had the power up. I also will always remember reading a comment by Matt Jackson, who in referencing the John McKittrick landing accident, that he could hear from the ground as the aircraft was coming in to land that the prop was set at full 3,000 RPM rather than the pre-prescribed 2,700 RPM - that there is enough of a difference in sound between just those prop settings alone to note, at least by a trained ear, from the ground.
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